Abstract
Cross-neutralization tests between 2 mouse-adapted strains of human poliomyelitis virus and Theiler''s virus of mouse encephalomyelitis and corresponding antiviral immune sera revealed overlapping reactions of various degrees between the three viruses. The immunological data are discussed in their bearing on the position of the experimentally adapted murine strains in relation to Theiler''s virus, on the one hand, and human poliomyelitis virus, on the other.